Display specification

[Adam Jackson]

On Monday 14 March 2005 12:10, Brian Paul wrote:
> Adam Jackson wrote:
> > So we want a device specifier.  Are PCI strings good enough?
> >
> > EGLDisplay dpy = eglGetDisplayForWidgetXXX("pci/0000:01:00.0");
> >
> > As long as there's a unique identifier for a device on a given bus, this
> > works, so basically that's everything except ISA.  Not very GL-ish to
> > pass a string in as an argument, I suppose.
>
> The sample code I'm working on does something like that.  I think it
> would be acceptable to pass a string.  Could we also have a more
> general syntax, like "screen/0" or "screen/1"?  That way we wouldn't
> tie the interface to PCI-based devices.

Sure, we probably should.  The reason for the pci/ part was so we could map 
this to other bus types.  MCA, SBus, and NuBus have addressable slots.  VLB 
and ISA don't, but there you could just say isa/0 and just live with only 
supporting on device on the ISA bus.  (Not that I know of any NuBus cards 
with 3D engines, but you may want to drive them with Mesa's swrast anyway.)

Bus-addresses are admittedly user-hostile.  So we need a mapping between 
'screen/0' and 'pci/01:00.0'.  And we can't just push that down into the 
driver because the driver we choose is based on the screen we're asking for.  
Neither do I really want an implicit mapping that depends on the order you 
walk the bus, because that can change (firmware upgrades, hotplugged cards, 
USB and PCMCIA displays).

Maybe that means a config file somewhere.  Anyway, nailing down the screen/ to 
bus address mapping isn't necessarily something we need to formalize within 
the API.

> The way I was thinking of it was:
>   - each card corresponds to an EGLDisplay
>   - an EGLDisplay may have one or more screens (i.e. pieces of glass)
>   - each screen may be a view onto different surface, or the same surface.

That sounds right to me.

- ajax
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